In recent years, various vehicular systems and devices such as an air-conditioner, a car audio system, a navigation system and the like are controlled by using an operation control unit. The operation control unit has an operation unit that is operated by a user, i.e., an occupant of a vehicle, for inputting various inputs for controlling those devices. The operation part of the air-conditioner for controlling an air amount, air temperature, or air-outlet positions, the operation part of the car audio system for controlling sound volume, or the like is, among other operation parts, provided as a dial controller (Refer to Japanese patent documents JP-A-H11-273506, JP-A-2000-67696, and JP-A-2001-184969).
The dial controller described in each of the above documents includes a supplemental devices such as a push switch, an LED indicator or the like in a center portion of an operation dial, where a rotation axis of the operation dial is located. The operation dials are usually arranged in a row on an instrument panel, and an interference between the supplemental devices of the two or more adjacent operation dials is prevented by having a rotation detection unit of the operation dial at an outer periphery of each operation dial. According to the description of the patent document JP-A-H11-273506, a rotation angle of the operation dial is detected by having a variable resistor that has a carbon film resistor printed on a substrate along the periphery of the operation dial. According to the description of the patent documents JP-A-2000-67696 and JP-A-2001-184969, a rotational movement of the operation dial is transferred to a rotary variable resistor by associating a small gear on a shaft of the variable resistor with a large gear on an outer circumference of the operation dial.
However, the structure of the operation dial disclosed in the patent document JP-A-H11-273506 requires a large arc shape carbon film resistor printed on the substrate that fittingly formed to be disposed on the instrument panel, which leads to an increased production cost of the substrate. In addition, an additional space for having the carbon film resistor consumes a limited space on the substrate, thereby reducing an installation space of other circuit elements and leading to a deteriorated space efficiency of the substrate. On the other hand, the disclosure in the patent documents JP-A-2000-67696 and JP-A-2001-184969 proposes the structure that requires the rotary variable resistor or the small gear that occupies a large planar space disposed at a position outside of the operation dial, thereby imposing restriction on the size and/or the design that arises from an increased planar space as a background space of the operation dial on the instrument panel. Furthermore, the increase of the background space of the operation dial is problematic when the plural operation dials need to be positioned in an area within a required distance for having the small gear or the like.